U.S. patent application number 13/699426 was filed with the patent office on 2013-08-08 for voltage converting circuit and electronic device.
This patent application is currently assigned to OMRON CORPORATION. The applicant listed for this patent is Tatsuakira Masaki, Misato Nabeto, Kenji Sakurrai, Hiroshi Sameshima, Hiroshi Tsuji. Invention is credited to Tatsuakira Masaki, Misato Nabeto, Kenji Sakurrai, Hiroshi Sameshima, Hiroshi Tsuji.
Application Number | 20130201742 13/699426 |
Document ID | / |
Family ID | 45401745 |
Filed Date | 2013-08-08 |
United States Patent
Application |
20130201742 |
Kind Code |
A1 |
Nabeto; Misato ; et
al. |
August 8, 2013 |
VOLTAGE CONVERTING CIRCUIT AND ELECTRONIC DEVICE
Abstract
A voltage converting circuit includes a plurality of first
capacitors that are charged by a power source, a second capacitor,
connected in parallel to the plurality of first capacitors, which
is able to be charged to a voltage that is supplied to a load
circuit, and a plurality of switching circuits, provided in such a
way as to correspond to the plurality of first capacitors, each of
which switches states of connection between its corresponding first
capacitor and the second capacitor. The first capacitors are
sequentially connected to the second capacitor through the
corresponding switching circuits as charging voltages of the first
capacitors reach a predetermined connection voltage that is higher
than a charging voltage of the second capacitor so that the first
capacitors are not short-circuited with each other.
Inventors: |
Nabeto; Misato; (Ikoma-shi,
JP) ; Sakurrai; Kenji; (Kizugawa-shi, JP) ;
Masaki; Tatsuakira; (Nara-shi, JP) ; Sameshima;
Hiroshi; (Nara-shi, JP) ; Tsuji; Hiroshi;
(Kyoto-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nabeto; Misato
Sakurrai; Kenji
Masaki; Tatsuakira
Sameshima; Hiroshi
Tsuji; Hiroshi |
Ikoma-shi
Kizugawa-shi
Nara-shi
Nara-shi
Kyoto-shi |
|
JP
JP
JP
JP
JP |
|
|
Assignee: |
OMRON CORPORATION
Kyoto
JP
|
Family ID: |
45401745 |
Appl. No.: |
13/699426 |
Filed: |
March 16, 2011 |
PCT Filed: |
March 16, 2011 |
PCT NO: |
PCT/JP2011/056279 |
371 Date: |
March 4, 2013 |
Current U.S.
Class: |
363/140 |
Current CPC
Class: |
H02M 7/04 20130101; H02M
3/07 20130101; H02M 2003/072 20130101 |
Class at
Publication: |
363/140 |
International
Class: |
H02M 7/04 20060101
H02M007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 2, 2010 |
JP |
2010-152436 |
Claims
1. A voltage converting circuit comprising: a plurality of first
capacitors configured to be charged by a power source; a second
capacitor, connected in parallel to the plurality of first
capacitors, capable of being charged to a voltage equal to a
voltage that is supplied to a load circuit; a plurality of
switching circuits, configured to correspond to the plurality of
first capacitors respectively, each switching circuit switches
states of connection between its corresponding first capacitor and
the second capacitor; and a connection control circuit configured
to sequentially connect the first capacitors to the second
capacitor through the corresponding switching circuits as charging
voltages of the first capacitors reach a predetermined connection
voltage that is higher than a charging voltage of the second
capacitor, and control a state of connection of each of the first
capacitors to the second capacitor so that the first capacitors are
not short-circuited with each other.
2. The voltage converting circuit according to claim 1, wherein the
predetermined connection voltage is a value of voltage that is
higher than the charging voltage of the second capacitor, at which
value of voltage a difference in voltage between the charging
voltage of each of the first capacitors and the charging voltage of
the second capacitor becomes such a difference in voltage that
efficiency of charge-transfer from the first capacitor to the
second capacitor becomes equal to or greater than a predetermined
level of efficiency.
3. The voltage converting circuit according to claim 1, further
comprising voltage monitoring circuits, configured to correspond to
the first capacitors respectively, each voltage monitoring circuit
monitors the charging voltage of its corresponding first capacitor,
wherein the connection control circuit carries out connection
control through the switching circuits in accordance with the
charging voltages of the first capacitors obtained by the voltage
monitoring circuits.
4. The voltage converting circuit according to claim 1, wherein the
connection control circuit sets a time constant required for each
of the first capacitors to be connected to the second capacitor
through its corresponding switching circuit to be longer than a
time constant required for the first capacitor to be disconnected
from the second capacitor through the switching circuit.
5. The voltage converting circuit according to claim 4, wherein the
connection control circuit causes one of the first capacitors to be
disconnected from the second capacitor through its corresponding
switching circuit at the same time as another one of the first
capacitor whose charging voltage has reached the predetermined
connection voltage is connected to the second capacitor through its
corresponding switching circuit.
6. The voltage converting circuit according to claim 1, wherein the
number of the plurality of first capacitors is such a number that a
total charging voltage of the plurality of first capacitors falls
within a voltage range corresponding to a predetermined percentage
of open-end voltage of the power source, at which percentage a
predetermined level of charging efficiency from the power source or
higher is attained.
7. The voltage converting circuit according to claim 3, wherein:
the number of the plurality of first capacitors is such a number
that a total charging voltage of the plurality of first capacitors
falls within a voltage range corresponding to a predetermined
percentage of open-end voltage of the power source, at which
percentage a predetermined level of charging efficiency from the
power source or higher is attained; and the predetermined
percentage is determined in accordance with an internal resistance
of each of the voltage monitoring circuits.
8. The voltage converting circuit according to claim 1, wherein the
number of the plurality of first capacitors is such a number that a
total charging voltage of the plurality of first capacitors is less
than or equal to half of an open-end voltage of the power source,
the number being greater than or equal to 2.
9. The voltage converting circuit according to claim 1, further
comprising a step-down converter connected in parallel to the
plurality of first capacitors and provided between the plurality of
first capacitors and the second capacitor, wherein the number of
the plurality of first capacitors is such a number that a voltage
stepped down through the plurality of first capacitors is
approximate to an input voltage of the step-down converter.
10. The voltage converting circuit according to claim 1, wherein
the power source includes a vibration electric power generation
device that converts external vibration energy into electric
power.
11. The voltage converting circuit according to claim 2, wherein
the predetermined level of efficiency is such a value that the
efficiency of charge-transfer from the first capacitor to the
second capacitor is equal to or greater than 85%.
12. An electronic device comprising: a voltage converting circuit
according to claim 1; and a load circuit; wherein the voltage
converting circuit causes an output voltage of the power source to
step down to a voltage that is supplied to the load circuit.
Description
TECHNICAL FIELD
[0001] The present invention relates to a voltage converting
circuit causing an output voltage of an AC power source to step
down to a voltage that is supplied to a load circuit, and an
electronic device including the same.
BACKGROUND ART
[0002] In keeping with a recent trend of energy saving, attention
has been given to environmental energy that does not depend on
fossil fuel or the like and exists ordinarily. Photovoltaic energy,
wind energy and the like have been widely known as environmental
energy. In addition, vibration energy existing around ordinarily
can be mentioned as environmental energy having an energy density
which is not inferior to that of the foregoing energy. In order to
supply, to a load circuit, electric power generated from this
vibration energy by an electric power generation device,
heretofore, a circuit for converting a voltage so as to be suitable
for the load circuit has been under study with regard to
improvement in its conversion efficiency.
[0003] For example, there has been disclosed a technique of
preventing reduction in voltage conversion efficiency in
consideration of a fact that it becomes difficult to realize a
desired voltage drop because of output impedance of a vibration
electric power generation device (refer to Patent Document 1).
According to this technique, switching circuits are provided for
switching, between series connection and parallel connection,
states of connection of a plurality of capacitors to a power source
circuit and a load circuit. Thus, the number of capacitors to be
connected by the switching circuits is controlled on the basis of
an input voltage from the power source circuit or a frequency of
the input voltage. Moreover, Patent Document 2 discloses a
technique for efficiently generating electric power from
small-amplitude vibrations. According to this technique, the ON/OFF
control of a switch for controlling an electric power output from a
vibration electric power generation device is carried out on the
basis of a cycle of vibrations, so that an electric power output
cycle is varied.
PRIOR ART DOCUMENTS
Patent Documents
[0004] Patent Document 1: Japanese Unexamined Patent Publication
No. 2009-124807
[0005] Patent Document 2: Japanese Unexamined Patent Publication
No. 2005-130624
[0006] Patent Document 3: Japanese Unexamined Patent Publication
No. 2005-198453
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0007] In a case of stepping down an output voltage of an AC power
source by charging a plurality of capacitors connected in series
once with the output voltage of the AC power source and then
simultaneously supplying the charged energy in these capacitors to
a load circuit connected in parallel to the capacitors, when the
capacitors are different in capacity from each other, it is
difficult to maintain efficiency of electric power supply from the
capacitors to the load circuit at an optimum state because of an
influence of the difference. Typically, it is difficult to exactly
adjust capacitors to be equal in capacity to each other. According
to the related art, therefore, it is difficult to maintain electric
power supply efficiency at a suitable state.
[0008] The present invention has been devised in view of the
foregoing problems, and an object thereof is to provide a voltage
converting circuit for bringing voltage conversion efficiency in a
case of stepping down an output voltage of an AC power source to a
voltage that is supplied to a load circuit into a suitable state as
soon as possible.
Means for Solving the Problems
[0009] According to the present invention, in order to solve the
foregoing problems, a voltage converting circuit to be provided
between an AC power source and a load circuit includes a plurality
of first capacitors that are charged by the power source, and a
second capacitor to which the first capacitors charged to a state
higher than a charging voltage of the second capacitor are
individually and sequentially connected. Thus, the second capacitor
is charged with good efficiency.
[0010] More specifically, the present invention provides a voltage
converting circuit including: a plurality of first capacitors that
are charged by a power source; a second capacitor, connected in
parallel to the plurality of first capacitors, which is able to be
charged to a voltage equal to a voltage that is supplied to a load
circuit; a plurality of switching circuits, provided in such a way
as to correspond to the plurality of first capacitors respectively,
each of which switches states of connection between its
corresponding first capacitor and the second capacitor; and a
connection control circuit for sequentially connecting the first
capacitors to the second capacitor through the corresponding
switching circuits as charging voltages of the first capacitors
reach a predetermined connection voltage that is higher than a
charging voltage of the second capacitor, and for controlling a
state of connection of each of the first capacitors to the second
capacitor so that the first capacitors are not short-circuited with
each other.
[0011] In the voltage converting circuit, the plurality of first
capacitors are charged by the power source, and the charging
voltages of the first capacitors correspond to distributed or
divided output voltages of the power source in accordance with
capacities of the first capacitors. Herein, all the capacities of
the plurality of first capacitors may be identical with each other.
Alternatively, the capacities of part of or all the first
capacitors may be different from each other. The term "identical"
used herein as to the capacities of the capacitors refers a
so-called nominal value, and therefore does not take variations in
capacity based on individual differences of the capacitors into
consideration.
[0012] The plurality of first capacitors are connected to the
second capacitor through the switching circuits corresponding to
the first capacitors respectively. That is, each of the first
capacitors is individually connected to or disconnected from the
second capacitor through its corresponding switching circuit. In
the voltage converting circuit according to the present invention,
the second capacitor may be configured to include one capacitor or
a plurality of capacitors. It is important herein to adopt the
configuration that the second capacitor is connected to or
disconnected from the plurality of first capacitors through the
switching circuits. It is only necessary to appropriately determine
the number of capacitors with which the second capacitor itself is
configured and to appropriately adopt a connection mode between the
capacitors.
[0013] Herein, the connection or disconnection of each of the first
capacitors to or from the second capacitor is controlled by the
connection control circuit. In order to charge the second
capacitor, the connection control circuit does not simultaneously
connect all the plurality of first capacitors to the second
capacitor, but determines, as a target to be connected to the
second capacitor, the first capacitor of which charging voltage
reaches the predetermined connection voltage that is higher than
the charging voltage of the second capacitor. That is, the
connection control circuit controls the connection or disconnection
of the first capacitor to or from the second capacitor so as to
realize suitable charging efficiency, in other words, suitable
voltage conversion efficiency at the time of electrical-charging
from the first capacitor to the second capacitor. As to the
connection by the connection control circuit, further, the states
of connection between the first capacitors and the second
capacitor, each of which satisfies the foregoing conditions, are
controlled so that the first capacitors are not short-circuited
with each other for the following reason. That is, suitable
electrical-charging to the second capacitor becomes difficult when
the first capacitors are short-circuited with each other.
[0014] By the adoption of the configuration that the connection
control circuit controls the states of connection between the first
capacitors and the second capacitor in accordance with a
correlation between the charging voltages of the plurality of first
capacitors and the charging voltage of the second capacitor, even
in the case where the variations in capacity of the first
capacitors become relatively great, the connection to the second
capacitor is controlled on the basis of the charging voltage of
each of the first capacitors. Thus, it is possible to eliminate an
influence due to the variations in capacity of the first capacitors
from the electrical-charging to the second capacitor as soon as
possible. By the control of the states of connection of the first
capacitors so as to prevent the first capacitors from being
short-circuited with each other, further, it is possible to realize
electrical-charging of the second capacitor from the power source
through the first capacitor and voltage conversion with suitable
efficiency.
Effect of the Invention
[0015] It becomes possible to bring voltage conversion efficiency
in a case of stepping down an output voltage of an AC power source
to a voltage that is supplied to a load circuit into a suitable
state as soon as possible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a diagram showing a schematic configuration of a
voltage converting circuit according to the present invention.
[0017] FIG. 2A is a first diagram showing a correlation between a
ratio of a total charging voltage of a first capacitor group to an
output voltage of a power source circuit and the efficiency of
electrical-charging.
[0018] FIG. 2B is a second diagram showing the correlation between
the ratio of the total charging voltage of the first capacitor
group to the output voltage of the power source circuit and the
efficiency of electrical-charging.
[0019] FIG. 2C is a third diagram showing the correlation between
the ratio of the total charging voltage of the first capacitor
group to the output voltage of the power source circuit and the
efficiency of electrical-charging.
[0020] FIG. 3 is a functional block diagram showing images of
functions to be exerted by the voltage converting circuit shown in
FIG. 1.
[0021] FIG. 4 is a diagram showing a correlation of efficiency of
charge-transfer from the first capacitors to the second capacitor
with regard to charging voltages of the first capacitors and the
charging voltage of the second capacitor.
[0022] FIG. 5 is a diagram concerning time constants during
connection and disconnection of the first capacitor to and from the
second capacitor in a case where electrical-charging from a power
source circuit to the second capacitor is carried out.
[0023] FIG. 6 is a timing chart showing the charging voltages of
the first capacitors, ON signals from switching circuits, and
transition of electric currents discharged from the first
capacitors to the second capacitor, in the voltage converting
circuit according to the present invention.
[0024] FIG. 7 is a diagram showing a correlation between the
charging efficiency of the voltage converting circuit according to
the present invention and the charging voltage of the second
capacitor.
[0025] FIG. 8 is a second diagram showing a schematic configuration
of the voltage converting circuit according to the present
invention.
MODE FOR CARRYING OUT THE INVENTION
[0026] With reference to the drawings, hereinafter, description
will be given of embodiments of a voltage converting circuit 1
according to the present invention. It is to be noted that
configurations to be described in the following embodiments are
merely illustrative; therefore, the present invention is not
intended to be limited to the configurations in the
embodiments.
Embodiment 1
[0027] FIG. 1 shows a schematic configuration of a voltage
converting circuit 1 provided between a load circuit 15 and a
vibration electric power generation device 11 that corresponds to
an AC power source in the present invention and generates electric
power with external vibrations used as a source. The voltage
converting circuit 1 includes a second capacitor 6 that steps down
an output voltage of the vibration electric power generation device
11 and accumulates the voltage as a drive voltage of the load
circuit 15. Herein, a power source circuit 10 is configured with
the vibration electric power generation device 11 and a
rectification circuit 12 that rectifies a current of electric power
generated by the vibration electric power generation device 11, and
an output of the power source circuit 10 is input to the voltage
converting circuit 1. Examples of the vibration electric power
generation device 11 may include electric power generation devices
utilizing an electret material. The vibration electric power
generation device is publicly known in the related art; therefore,
the detailed description thereof will not be given in the
specification. Moreover, the power source circuit 10 may include an
electric power generation device other than the vibration electric
power generation device. The vibration electric power generation
device adopted in this embodiment utilizes an electret material so
as to have an electric power generation amount of 20 to 100 .mu.W
and an output voltage of 30 to 80 Vp-p; however, the application of
the present invention is not limited to this device.
[0028] Further, a switching circuit 16 is provided between the
voltage converting circuit 1 and the load circuit 15 to supply, to
the load circuit 15, energy accumulated in the second capacitor 6
of the voltage converting circuit 1.
[0029] In the voltage converting circuit 1, an output terminal of
the power source circuit 10 is connected to a first capacitor group
2 including a plurality of first capacitors connected in series,
and an output of the output terminal is input to the first
capacitors 21 to 23 in the first capacitor group 2. In this
embodiment, the number of first capacitors to be included in the
first capacitor group 2 is three, but is adjusted as appropriate in
consideration of voltage conversion efficiency (charging
efficiency) and the like as will be described later. It is assumed
herein that the first capacitors 21 to 23 are equal in capacity to
each other.
[0030] Moreover, wiring is carried out so that the second capacitor
6 is able to be connected in parallel to the three first capacitors
21 to 23 in the first capacitor group 2, and switching circuits are
provided between the first capacitors and the second capacitor 6 in
such a way as to correspond to the first capacitors respectively,
and switch states of connection or disconnection of the first
capacitors to or from the second capacitor 6. More specifically,
the switching circuits 71a and 71b are provided between the first
capacitor 21 and the second capacitor 6, the switching circuits 72a
and 72b are provided between the first capacitor 22 and the second
capacitor 6, and the switching circuits 73a and 73b are provided
between the first capacitor 23 and the second capacitor 6. The
switch operations of these switching circuits are individually
controlled in accordance with charging voltages of the
corresponding first capacitors, and the like, as will be described
later, and switching adjustment circuits 41 to 43 are provided in
such a way as to correspond to the first capacitors, respectively,
in order to control the switching operations.
[0031] Moreover, voltage monitoring circuits 31 to 33 are provided
in such a way as to correspond to the three first capacitors 21 to
23 in the first capacitor group 2, respectively, in order to
monitor the charging voltages of the first capacitors 21 to 23. The
charging voltages of the first capacitors, which are detected by
the voltage monitoring circuits 31 to 33, are transferred to a
switchover control circuit 5. The switchover control circuit 5
controls the switching operations of the switching circuits 71a to
73b through the switching adjustment circuits 41 to 43, on the
basis of the transferred charging voltage of each of the first
capacitors and a charging voltage of the second capacitor 6.
Accordingly, the switchover control circuit 5 and the switching
adjustment circuits 41 to 43 correspond to a connection control
circuit according to the present invention. Moreover, an upper
limit voltage control circuit (not shown) is provided beside the
second capacitor 6. This upper limit voltage control circuit
controls an upper limit voltage (e.g., 3 to 3.15 V) of the second
capacitor 6 so that excessive voltage is not applied to the load
circuit 15 in a case where accumulated energy is supplied to the
load circuit 15. In this embodiment, accordingly, the second
capacitor 6 is charged by the power source circuit 10 so as to be
maintained at a state in which the second capacitor 6 is charged at
an almost upper limit voltage.
[0032] During the operation of the voltage converting circuit 1,
the first capacitor group 2 is in a state constantly connected to
the power source circuit 10 as shown in FIG. 1. Therefore, each of
the first capacitors is constantly charged by the power source
circuit 10 in accordance with electric power supply (vibration
electric power generation) from the vibration electric power
generation device 11 in the power source circuit 10. Herein,
charging efficiency between the vibration electric power generation
device 11 and the first capacitor group varies depending on a ratio
between an open-end voltage of the vibration electric power
generation device 11 and a total charging voltage of the first
capacitor group 2 (first voltage ratio).
[0033] Herein, the charging efficiency Ec1 between the vibration
electric power generation device 11 and the first capacitor group
is represented by the following equation.
Ec1=(amount of energy accumulated in first capacitor group per unit
time)/(amount of electric power supplied(generated)by vibration
electric power generation device 11 with matched resistance)
[0034] Plotting theoretical correlations between the charging
efficiency Ec1 defined as described above and the first voltage
ratio allows depiction of a parabola having an extreme value
obtained when the first voltage ratio is 50% as shown with a line
L1 in FIG. 2A. Accordingly, it is only necessary to determine the
number of first capacitors to be included in the first capacitor
group 2 so that the total charging voltage of the first capacitor
group 2 is half of the open-end voltage of the vibration electric
power generation device 11. Herein, the charging voltage of each of
the first capacitors varies when electrical-discharging is carried
out by the switching operation of the switching circuit 71a (which
will be described later) or the like. Therefore, the total charging
voltage of the first capacitor group 2 may be tentatively
calculated as follows using an equation V1ave(=(V1+V1')/2) in which
V1 represents a charging voltage at an initial phase of
electrical-charging from one of the first capacitors (e.g., the
first capacitor 21) to the second capacitor 6 by the switching
operation in the first capacitor (a charging initial timing), V1'
represents a charging voltage at a terminal timing of the same
electrical-charging (a charging terminal timing), and V1ave
represents an average value of the two voltages.
Total charging voltage of first capacitor group 2=n.times.V1ave
[0035] (n: the number of first capacitors in first capacitor group
2, n=3 in this embodiment)
[0036] Typically, a capacitor to be available in the market has a
capacity set at a specific value. Therefore, it is difficult to
determine the number of first capacitors to be included in the
first capacitor group 2 so that the total charging voltage of the
first capacitor group 2 is exactly the half (50%) of the open-end
voltage of the vibration electric power generation device 11 in
some cases. In such a case, it is only necessary to determine the
number of first capacitors to be included in the first capacitor
group 2 so that the total charging voltage of the first capacitor
group 2 approaches the half of the open-end voltage of the
vibration electric power generation device 11 as soon as
possible.
[0037] On the other hand, in a case where a load resistor is
connected to the first capacitor group 2, the first voltage ratio
at the time when the charging efficiency reaches the extremal value
becomes lower than 50% as shown with a line L2 in FIG. 2B or a line
L3 in FIG. 2C. FIG. 2B is a diagram showing transition of the
charging efficiency in the state in which the load resistors to be
connected to the first capacitors have a value of about 10 M.OMEGA.
in the case where the vibration electric power generation device 11
to be used herein has an internal resistance of 10 M.OMEGA. to 20
M.OMEGA.. FIG. 2C is a diagram showing transition of the charging
efficiency in the state in which the load resistors to be connected
to the first capacitors have a value of about 100 M.OMEGA. in the
case where the vibration electric power generation device 11 to be
used herein is similar to that shown in FIG. 2B. For reference, a
line L4 in FIG. 2B and a line L5 in FIG. 2C each indicate electric
power consumption efficiency in the load resistor. The extreme
value of the charging efficiency varies as described above because
the first capacitor supplies energy to the load resistor connected
thereto while accumulating energy therein. In the voltage
converting circuit 1 shown in FIG. 1, the voltage monitoring
circuits 31 to 33 are connected to the first capacitors in the
first capacitor group 2, respectively, and correspond to the load
resistors. In the voltage converting circuit 1, accordingly, it is
only necessary to determine the number of first capacitors to be
included in the first capacitor group 2 in consideration of the
internal resistance of each of the voltage monitoring circuits 31
to 33.
[0038] With reference to FIG. 3, description will be given of a
charging operation to be carried out from the vibration electric
power generation device 11 to the second capacitor 6 in the voltage
converting circuit 1 configured as described above. The charging
operation is carried out by the switchover control circuit 5
together with the voltage monitoring circuits 31 to 33 and the
switching adjustment circuits 41 to 43. Thus, the output voltage of
the power source circuit 10 is stepped down to the charging voltage
of the second capacitor 6 so as to correspond to the drive voltage
of the load circuit 15. FIG. 3 is a functional block diagram
showing images of functions to be exerted by the voltage monitoring
circuits 31 to 33, the switching adjustment circuits 41 to 43 and
the switchover control circuit 5. As a matter of course, each
circuit may have a functional part other than the functional part
shown in FIG. 3.
[0039] The voltage monitoring circuits 31 to 33 are configured with
a charging voltage monitoring part 101, a switching switchover
requesting part 102 and a discharging termination notifying part
103. The charging voltage monitoring parts 101 constantly monitor
the charging voltages of the first capacitors 21 to 23 to which the
voltage monitoring circuits 31 to 33 correspond respectively. A
value of the charging voltage of each of the first capacitors,
which is acquired by this monitoring, is transferred to the
switchover control circuit 5 at an appropriate timing. The
switching switchover requesting parts 102 switch the corresponding
switching circuits 71a to 73b in order to transfer the energy
stored in the first capacitors to the second capacitor 6, and issue
switchover requests to the switchover control circuit 5 in order to
connect the relevant first capacitors to the second capacitor 6.
Herein, a condition that this switchover request is issued is a
case where a correlation between the charging voltage of each of
the first capacitors 21 to 23 and the charging voltage of the
second capacitor 6 satisfies a predetermined condition, and the
detailed description of the predetermined condition will be given
later. Next, when the charging voltage of the first capacitor is
reduced to a predetermined threshold value by the supply of
electric power from the first capacitor to the second capacitor 6,
the discharging termination notifying part 103 notifies the
switchover control circuit 5 of the termination of
electrical-discharging.
[0040] Next, the switchover control circuit 5 is configured with a
switchover priority determining part 201, a connection state
verifying part 202, a connection permitting part 203 and a
disconnection instructing part 204. The switchover priority
determining part 201 determines the priority of connections of the
plurality of first capacitors 21 to 23 to the second capacitor 6 so
that the plurality of first capacitors 21 to 23 are not
simultaneously connected to the second capacitor 6 by the switching
circuits 71a to 73b, that is, the first capacitors are not
short-circuited with each other. Herein, the first capacitor
serving as a target of the switchover priority determining part 201
is the first capacitor receiving the switchover request from the
switching switchover requesting part 102. The connection state
verifying part 202 verifies which first capacitor is connected to
the second capacitor 6. The connection permitting part 203 permits
the connection of the first capacitor to the second capacitor 6 on
the basis of the status verified by the connection state verifying
part 202. The disconnection instructing part 204 issues a
disconnection instruction to the switching adjustment circuits 41
to 43 so as to disconnect the target first capacitor from the
second capacitor 6, on the basis of the notification from the
discharging termination notifying part 103.
[0041] Next, each of the switching adjustment circuits is
configured with a switching executing part 301. The switching
executing part 301 controls the switching operation of the
corresponding one of the switching circuits 71a to 73b in
accordance with a permission signal from the connection permitting
part 203 or the disconnection instruction from the disconnection
instructing part 204.
[0042] By virtue of the voltage monitoring circuits 31 to 33, the
switchover control circuit 5 and the switching adjustment circuits
41 to 43, each of which is configured as described above, the
second capacitor 6 is charged with the output voltage of the
vibration electric power generation device 11 by execution of the
following process in the voltage converting circuit 1. It is to be
noted that an order of the following process items (1) to (5) is
not limitative, but may be appropriately adjusted within a range
which does not deviate from the gist of the present invention.
CHARGING PROCESS
[0043] (1) An output current from the power source circuit 10 is
stored in each of the first capacitors in the first capacitor group
2. Thus, the charging voltage of each of the first capacitors
rises. The variations in charging voltage of the first capacitors
are monitored by the charging voltage monitoring parts 101 of the
corresponding voltage monitoring circuits.
[0044] (2) When the charging voltage of each of the first
capacitors, which is monitored by the charging voltage monitoring
part 101, reaches a predetermined connection voltage serving as a
standard, the switching switchover requesting part 102 sends a
switchover request to the switchover control circuit 5.
[0045] Herein, the predetermined connection voltage is determined
so that efficiency of charge-transfer from each of the first
capacitors to the second capacitor 6 is a favorable value when each
of the first capacitors is connected to the second capacitor 6.
With reference to FIG. 4, then, description will be given for the
determination of the predetermined connection voltage. FIG. 4
shows, for each charging voltage of the capacitor, the efficiency
of charge-transfer from the first capacitor to the second capacitor
at the time when the first capacitor is connected to the second
capacitor. This charge-transfer efficiency is theoretically
calculated from the following equation.
Charge-transfer efficiency=(increase in the amount of energy in
second capacitor by connection)/(decrease in the amount of energy
in first capacitor)
[0046] In FIG. 4, an upper table (a) shows a case where the first
capacitor and the second capacitor each have a capacity of 10
.mu.F, and a lower table (b) shows a case where the first capacitor
has a capacity of 1 .mu.F and the second capacitor has a capacity
of 10,000,000 .mu.F. The charging voltage of each of the capacitors
in an initial phase corresponds to the charging voltage at the
timing of start of the connection, and the charging voltage of each
of the capacitors in a terminal phase corresponds to the charging
voltage at the timing of termination of the connection and then
disconnection. As it is clear in FIG. 4, the charge-transfer
efficiency tends to increase as a difference in voltage between the
charging voltage of the first capacitor and the charging voltage of
the second capacitor in the initial phase becomes small
irrespective of the capacities of the first and second
capacitors.
[0047] In this embodiment, therefore, it is assumed that the
charge-transfer from the first capacitor to the second capacitor is
carried out, that is, the switchover request is sent to the
switchover control circuit 5 in a case where the difference in
voltage between the first capacitor and the second capacitor is
such a difference in voltage that the charging voltage of the first
capacitor in the initial phase becomes about 1.1 to 1.2 times as
large as the charging voltage of the second capacitor in the
initial phase so that the efficiency of charge-transfer reaches
about 85% or higher. More specifically, as described above, the
upper limit voltage control circuit is provided beside the second
capacitor 6 to maintain the charging voltage of the second
capacitor 6 at about 3 to 3.15 V. In this embodiment, therefore,
the predetermined connection voltage is set at about 3.3 V.
[0048] (3) The switchover priority determining part 201 determines
the priority of connections of the first capacitors 21 to 23 to be
connected to the second capacitor 6, in accordance with the
switchover request from the switching switchover requesting part
102 of each of the voltage monitoring circuits. In principle, the
connection priority is given in the order in which the switchover
request is received. In a case where there is a possibility that
the plurality of first capacitors are simultaneously connected in a
period in which the states of connection are maintained, the
connection priority is given in the order of the first capacitor
21, the first capacitor 22 and the first capacitor 23. The method
for giving the connection priority is not limited to that described
above. It is important to give the connection priority so that two
or more first capacitors are not simultaneously connected to the
second capacitor 6.
[0049] (4) The connection state verifying part 202 determines which
first capacitor is connected to the second capacitor 6. When it is
determined that no first capacitor is connected to the second
capacitor 6, the connection permitting part 203 issues an
instruction of permitting to connect the first capacitor, to which
the highest connection priority is given, to the second capacitor 6
to the switching circuit corresponding to this first capacitor.
Then, the switching executing part 301 of the switching circuit
connects the first capacitor to the second capacitor 6. Thus, the
second capacitor 6 is charged. On the other hand, when it is
determined that any of the first capacitors is connected to the
second capacitor 6, the connection permitting part 203, which
issues an instruction of permitting the connection, is brought into
a standby state until receiving a notification about termination of
electrical-discharging from the discharging termination notifying
part 103 of the voltage monitoring circuit corresponding to the
first capacitor connected to the second capacitor 6.
[0050] The discharging termination notifying part 103 issues the
notification about the termination of electrical-discharging at the
time when the charging voltage of the first capacitor is
approximate to the charging voltage of the second capacitor 6. When
the discharging termination notifying part 103 issues the
notification about the termination of electrical-discharging, the
disconnection instructing part 204 issues a disconnection
instruction for disconnecting the first capacitor from the second
capacitor 6, to the switching circuit corresponding to the first
capacitor connected to the second capacitor 6. When the switching
circuit receives the disconnection instruction, the switching
executing part 301 thereof disconnects the first capacitor from the
second capacitor. At the same time as this disconnection, the
switching circuit corresponding to the first capacitor to be
connected to the second capacitor 6 next executes the connection
between these capacitors.
[0051] In FIG. 5, an upper graph (a) shows state transition
concerning the connection of the first capacitor to the second
capacitor at the time of the connection or disconnection by the
switching circuit. In this embodiment, a connection time constant
.DELTA.t1 in a case where the switching executing part 301 brings
the switching circuit into a connected state (an ON state) is set
to be relatively longer than a disconnection time constant
.DELTA.t2 in a case where the switching executing part 301 brings
the switching circuit into a disconnected state (an OFF state). For
example, ".DELTA.t1" is about 7 msec and ".DELTA.t2" is
approximately 0 msec as soon as possible. As described above, the
charge-transfer is carried out gently by setting the connection
time constant to be relatively longer. Therefore, even in the case
where one switching circuit carries out the disconnecting process
while the different switching circuit carries out connecting
process, it becomes possible to prevent the first capacitors
corresponding to the respective switching circuits from being
short-circuited with each other. As the result, even in the case
where the disconnecting process by one switching circuit and the
connecting process by the different switching circuit are carried
out simultaneously, it is possible to substantially prevent the
first capacitors from being short-circuited with each other.
[0052] As shown in a lower graph (b) of FIG. 5, on the other hand,
both the connection time constant .DELTA.t1 and the disconnection
time constant .DELTA.t2 are set to be approximately 0 msec as soon
as possible. Herein, when the disconnecting process by one
switching circuit and the connecting process by the different
switching circuit are carried out simultaneously or when the two
processes are carried out at considerably short intervals, there is
a high possibility that the first capacitors are short-circuited
with each other. In the voltage converting circuit 1 according to
the present invention, particularly, it is important to set the
connection time constant .DELTA.t1 and the disconnection time
constant .DELTA.t2 each of which is able to prevent the first
capacitors from being short-circuited with each other in
consideration of a fact that it is crucial to connect substantially
only one first capacitor to the second capacitor 6.
[0053] (5) The items (1) to (4) are carried out repeatedly as
appropriate. Thus, the first capacitors having the charging voltage
reaching the predetermined connection voltage are sequentially
connected to the second capacitor so that the first capacitors are
not short-circuited with each other. As the result, the second
capacitor is charged in the state in which the efficiency of
charge-transfer from the first capacitor to the second capacitor is
maintained at 85% or higher. As described above, further, the
charging efficiency from the vibration electric power generation
device 11 to the first capacitor group 2 is also maintained at a
favorable value. Therefore, the voltage dropping down efficiency
and the charging efficiency from the vibration electric power
generation device 11 to the second capacitor become considerably
favorable as the entire voltage converting circuit 1. Moreover, the
charge-transfer to the second capacitor is carried out while the
charging voltage of each of the first capacitors is monitored.
Therefore, appropriate electrical-charging to the second capacitor
is realized even when the first capacitors are different in
capacity from each other in some degree.
[0054] In consideration of the foregoing description, FIG. 6 shows
a timing chart of the operations of the voltage converting circuit
1. To simplify the description, the number of first capacitors is
two in this timing chart. In FIG. 6, upper two lines indicate
transition of the charging voltages of the two first capacitors,
next two lines indicate variation in the states of connection of
the switching circuits corresponding to the two first capacitors,
next two lines indicate transition of currents discharged from the
two first capacitors to the second capacitor, and a lowermost line
indicates transition of the charging voltage of the second
capacitor. At an overlapping timing in FIG. 6, the voltage
monitoring circuits corresponding to the two first capacitors
simultaneously issue the switchover requests (see a dotted circle
in FIG. 6). Therefore, the connection start timing of one of the
first capacitors (the lower-side first capacitor) is intentionally
shifted from the timing at which the switchover request is issued.
Thus, it is possible to prevent the first capacitors from being
short-circuited with each other. At this overlapping timing, energy
is not discharged from the first capacitor of which the connection
start timing is shifted, and this first capacitor is connected to
the power source circuit 10. Therefore, the charging voltage of
this first capacitor has a peak value which is slightly higher than
a peak value of the charging voltage at a timing other than the
overlapping timing.
[0055] In FIG. 7, an upper portion (a) shows a comparison between
the charging efficiency of the entire voltage converting circuit 1
according to the present invention and charging efficiency of a
voltage converting circuit according to the related art, and a
lower portion (b) shows a schematic configuration of the voltage
converting circuit according to the related art. According to the
related art, an output voltage of a power source circuit is
directly applied to a capacitor. As it is apparent from the upper
portion (a) of FIG. 7, it is considered that the charging
efficiency of the voltage converting circuit 1 according to the
present invention exceeds 50%, which is considerably high, and is
excellent in practical use.
MODIFIED EXAMPLE 1
[0056] In the foregoing embodiment, all the first capacitors in the
first capacitor group 2 are identical in capacity with each other.
Typically, a capacitor to be available in the market has a capacity
limited to a specific value. On the condition that all the first
capacitors are identical in capacity with each other, therefore, it
is not necessarily easy to set the first voltage ratio at a
predetermined value so that the efficiency of electrical-charging
from the vibration electric power generation device 11 to the first
capacitor group 2 is adjusted to be optimum as shown in FIGS. 2A to
2C. Hence, the capacities of part of the plurality of first
capacitors in the first capacitor group 2, preferably, the capacity
of one first capacitor (hereinafter, referred to as "first
capacitor for adjustment") is set to be different from those of the
remaining first capacitors (hereinafter, referred to as "standard
first capacitor"). Thus, it is possible to further approximate the
first voltage ratio to the predetermined value and to optimize the
efficiency of electrical-charging from the vibration electric power
generation device 11 to the first capacitor group 2.
[0057] In this case, the charging voltage of the first capacitor
for adjustment at the time of the charge-transfer by the switching
circuit should be higher than the charging voltage of the second
capacitor 6. In order that the efficiency of charge-transfer from
the standard first capacitor to the second capacitor 6 is set to be
favorable, moreover, the foregoing correlation (charging voltage of
standard first capacitor=charging voltage of second capacitor
6.times.1.1 to 1.2) is maintained between the charging voltage of
the standard first capacitor and the charging voltage of the second
capacitor 6. Therefore, there is a possibility that the correlation
is no longer applicable between the charging voltage of the first
capacitor for adjustment and the charging voltage of the second
capacitor 6. However, since the efficiency of electrical-charging
from the vibration electric power generation device 11 to the first
capacitor group 2 is optimized by the use of the first capacitor
for adjustment, the second capacitor 6 can be efficiently charged
as the entire voltage converting circuit 1 in some cases.
MODIFIED EXAMPLE 2
[0058] In the foregoing embodiment, the second capacitor 6 is
configured with one capacitor, but may be configured with a
plurality of capacitors. Moreover, the capacitors may be connected
in series or in parallel, and the connection mode of the capacitors
may be a combination of the series connection and the parallel
connection. With regard to the foregoing correlation between the
charging voltage of each of the first capacitors and the charging
voltage of the second capacitor 6, when such a correlation is
established between the entire second capacitor configured with a
plurality of capacitors and the first capacitor, efficient
charge-transfer can be carried out from the first capacitor to the
entire second capacitor. Moreover, when the connection mode between
the load circuit 15 and the plurality of capacitors, with which the
second capacitor is configured, is appropriately adjusted, the
voltage converting circuit 1 is able to have a plurality of output
voltages for the load circuit 15.
Embodiment 2
[0059] With reference to FIG. 8, description will be given of a
second embodiment of the voltage converting circuit 1 according to
the present invention. In the voltage converting circuit 1
according to this embodiment, as shown in FIG. 8, a step-down
converter 8 is provided between the first capacitor group 2 and the
second capacitor 6. Accordingly, a voltage stepped down by the
first capacitor group 2 is input to the step-down converter 8.
Then, the voltage is further stepped down by the step-down
converter 8 and is input to the second capacitor 6. Typically, an
amount of electric power to be consumed by the step-down converter
8 is relatively large. However, the step-down converter 8 is
allowed to reduce the degree of a voltage drop in the first
capacitor group 2. Therefore, it is possible to reduce the number
of first capacitors to be included in the first capacitor group 2
and to realize size reduction of the circuit.
[0060] It is to be noted that the number of first capacitors in
this embodiment is determined in such a way that the output voltage
of the power source circuit 10 corresponds to the input voltage of
the step-down converter 8. Herein, it is preferred that the voltage
stepped down through the first capacitor group 2 is set at a value
of the input voltage of the step-down converter 8 or is set at a
value approximate to the input voltage within such a range that the
operation of the step-down converter is not hindered. According to
the configuration shown in FIG. 8, the step-down converter 8 allows
reduction in number of the first capacitors to be included in the
first capacitor group 2 from three in the foregoing embodiment to
two.
Embodiment 3
[0061] In a third embodiment of the voltage converting circuit 1
according to the present invention, priority is given to reduction
in size of the voltage converting circuit 1 rather than
optimization of the efficiency of electrical-charging from the
vibration electric power generation device 11 to the first
capacitor group 2, and the number of first capacitors to be
included in the first capacitor group 2 may be set in accordance
with the size of the voltage converting circuit 1. In such a case,
preferably, in order that the efficiency of charge-transfer between
each of the first capacitors and the second capacitor is set to be
favorable, the foregoing correlation (charging voltage of first
capacitor=charging voltage of second capacitor 6.times.1.1 to 1.2)
is maintained between the charging voltage of each of the first
capacitors and the charging voltage of the second capacitor 6.
[0062] According to the present invention, as described above, a
voltage converting circuit to be provided between an AC power
source and a load circuit includes a plurality of first capacitors
that are charged by the power source, and a second capacitor to
which the first capacitors charged to a state higher than a
charging voltage of the second capacitor are individually and
sequentially connected. Thus, the second capacitor is charged with
good efficiency.
[0063] More specifically, the present invention provides a voltage
converting circuit including: a plurality of first capacitors that
are charged by a power source; a second capacitor, connected in
parallel to the plurality of first capacitors, which is able to be
charged to a voltage equal to a voltage that is supplied to a load
circuit; a plurality of switching circuits, provided in such a way
as to correspond to the plurality of first capacitors respectively,
each of which switches states of connection between its
corresponding first capacitor and the second capacitor; and a
connection control circuit for sequentially connecting the first
capacitors to the second capacitor through the corresponding
switching circuits as charging voltages of the first capacitors
reach a predetermined connection voltage that is higher than a
charging voltage of the second capacitor, and for controlling a
state of connection of each of the first capacitors to the second
capacitor so that the first capacitors are not short-circuited with
each other.
[0064] In the voltage converting circuit, the plurality of first
capacitors are charged by the power source, and the charging
voltages of the first capacitors correspond to distributed or
divided output voltages of the power source in accordance with
capacities of the first capacitors. Herein, all the capacities of
the plurality of first capacitors may be identical with each other.
Alternatively, the capacities of part of or all the first
capacitors may be different from each other.
[0065] The plurality of first capacitors are connected to the
second capacitor through the switching circuits corresponding to
the first capacitors respectively. That is, each of the first
capacitors is individually connected to or disconnected from the
second capacitor through its corresponding switching circuit. In
the voltage converting circuit according to the present invention,
the second capacitor may be configured to include one capacitor or
a plurality of capacitors. It is important herein to adopt the
configuration that the second capacitor is connected to or
disconnected from the plurality of first capacitors through the
switching circuits. It is only necessary to appropriately determine
the number of capacitors with which the second capacitor itself is
configured and to appropriately adopt a connection mode between the
capacitors.
[0066] Herein, the connection or disconnection of each of the first
capacitors to or from the second capacitor is controlled by the
connection control circuit. In order to charge the second
capacitor, the connection control circuit does not simultaneously
connect all the plurality of first capacitors to the second
capacitor, but determines, as a target to be connected to the
second capacitor, the first capacitor of which charging voltage
reaches the predetermined connection voltage that is higher than
the charging voltage of the second capacitor. That is, the
connection control circuit controls the connection or disconnection
of the first capacitor to or from the second capacitor so as to
realize suitable charging efficiency, in other words, suitable
voltage conversion efficiency at the time of electrical-charging
from the first capacitor to the second capacitor. As to the
connection by the connection control circuit, further, the states
of connection between the first capacitors and the second
capacitor, each of which satisfies the foregoing conditions, are
controlled so that the first capacitors are not short-circuited
with each other for the following reason. That is, suitable
electrical-charging to the second capacitor becomes difficult when
the first capacitors are short-circuited with each other.
[0067] By the adoption of the configuration that the connection
control circuit controls the states of connection between the first
capacitors and the second capacitor in accordance with a
correlation between the charging voltages of the plurality of first
capacitors and the charging voltage of the second capacitor, even
in the case where the variations in capacity of the first
capacitors become relatively great, the connection to the second
capacitor is controlled on the basis of the charging voltage of
each of the first capacitors. Thus, it is possible to eliminate an
influence due to the variations in capacity of the first capacitors
from the electrical-charging to the second capacitor as soon as
possible. By the control of the states of connection of the first
capacitors so as to prevent the first capacitors from being
short-circuited with each other, further, it is possible to realize
electrical-charging to the second capacitor from the power source
through the first capacitor and voltage conversion with suitable
efficiency.
[0068] In the voltage converting circuit, the predetermined
connection voltage may be a value of voltage that is higher than
the charging voltage of the second capacitor, at which value of
voltage a difference in voltage between the charging voltage of
each of the first capacitors and the charging voltage of the second
capacitor becomes such a difference in voltage that efficiency of
charge-transfer from the first capacitor to the second capacitor
reaches a predetermined level of efficiency or higher. That is, the
predetermined connection voltage is determined in consideration of
a fact that the difference in voltage between the charging voltage
of each of the first capacitors and the charging voltage of the
second capacitor exerts an influence on efficiency of
charge-transfer from the first capacitor to the second capacitor.
It can be found that the charge-transfer efficiency tends to
decrease when the charging voltage of each of the first capacitors
rises with respect to the charging voltage of the second capacitor,
in other words, when the difference in voltage becomes large. This
tendency does not change basically even when the first capacitor is
different in capacity from the second capacitor. Therefore, it is
preferred that the predetermined connection voltage for
determination to be connected to the second capacitor by the
connection control circuit is determined in consideration of the
tendency of the charge-transfer efficiency. Experimentally, it is
preferred that the predetermined connection voltage is about 1.1 to
1.2 times as large as the charging voltage of the second capacitor,
at which voltage the predetermined efficiency becomes 85% or
higher.
[0069] Herein, the voltage converting circuit may further include
voltage monitoring circuits, provided in such a way as to
correspond to the first capacitors respectively, each of which
monitors the charging voltage of its corresponding first capacitor.
In this case, the connection control circuit carries out connection
control through the switching circuit in accordance with the
charging voltages of the first capacitors as obtained by the
voltage monitoring circuits, respectively. Thus, it is possible to
favorably maintain the efficiency of electrical-charging from the
first capacitor to the second capacitor.
[0070] In the voltage converting circuit, preferably, the
connection control circuit sets a time constant required for each
of the first capacitors to be connected to the second capacitor
through its corresponding switching circuit to be longer than a
time constant required for the first capacitor to be disconnected
from the second capacitor through the switching circuit. When the
connection time constant is set to be longer than disconnection
time constant, charges are gradually transferred from the first
capacitor. Therefore, the first capacitors are apt to be prevented
from being short-circuited with each other when the connection
control circuit sequentially connects the first capacitors to the
second capacitor. Herein, it is only necessary to appropriately set
the length of the connection time constant relative to the
disconnection time constant in view of the prevention of
short-circuit between the first capacitors. Moreover, it is
preferred that the disconnection time constant is set at such a
value that the first capacitor is disconnected from the second
capacitor as soon as possible, in order to sequentially connect the
first capacitors to the second capacitor with good efficiency.
[0071] By setting the connection time constant to be relatively
long as described above, the connection control circuit may set the
disconnection timing of the switching circuit corresponding to the
first capacitor connected to the second capacitor to be the same
timing as the connection timing of the switching circuit
corresponding to the different first capacitor of which the
charging voltage reaches the predetermined connection voltage. By
setting the connection time constant as described above, it is
possible to prevent the first capacitors from being short-circuited
with each other even when the disconnection timing of one of the
first capacitors is set to be the same timing as the connection
timing of the different first capacitor.
[0072] In the voltage converting circuit, the number of the
plurality of first capacitors may be such a number that a total
charging voltage of the plurality of first capacitors falls within
a voltage range corresponding to a predetermined percentage of
open-end voltage of the power source, at which percentage a
predetermined level of charging efficiency from the power source or
higher is attained. The total charging voltage of the plurality of
first capacitors rises in accordance with the number of first
capacitors. With regard to electrical-charging from the power
source to each of the first capacitors, it is theoretically known
that when a ratio of the total charging voltage of the plurality of
first capacitors to the open-end voltage of the power source
(hereinafter, referred to as "first voltage ratio") is approximate
to 50%, the efficiency of electrical-charging from the power source
to the first capacitor has a generally favorable value (the
predetermined charging efficiency). However, the first voltage
ratio in which the charging efficiency is set at the predetermined
charging efficiency varies because of an influence of internal
resistance and the like in the power source and the plurality of
first capacitors. Therefore, it is preferred that the predetermined
percentage of the first voltage ratio is determined in
consideration of this variation. Herein, the number of the
plurality of first capacitors may be previously set in a fixed
manner in accordance with the open-end voltage of the power source,
and the like. Alternatively, the number may be adjusted in a
variable manner in accordance with the change of the open-end
voltage, and the like.
[0073] In the case where the voltage converting circuit includes
the voltage monitoring circuit as described above, the internal
resistance of this voltage monitoring circuit exerts an influence
on the determination of the predetermined percentage. Therefore, it
is preferred that the first voltage ratio for setting the charging
efficiency at the predetermined charging efficiency is determined
in consideration of the internal resistance of the voltage
monitoring circuit.
[0074] In the voltage converting circuit, the number of the
plurality of first capacitors is such a number that a total
charging voltage of the plurality of first capacitors is less than
or equal to half of an open-end voltage of the power source, the
number being greater than or equal to 2. That is, it is possible to
realize size reduction of the voltage converting circuit by
reducing the number of first capacitors in consideration of the
decrease of the efficiency of electrical-charging from the power
source to each of the first capacitors.
[0075] Moreover, the voltage converting circuit may further include
a step-down converter connected in parallel to the plurality of
first capacitors and provided between the plurality of first
capacitors and the second capacitor. In this case, the number of
the plurality of first capacitors may be such a number that a total
charging voltage of the plurality of first capacitors is
approximate to an input voltage of the step-down converter. It is
possible to realize an optimum design, particularly, size reduction
of the voltage converting circuit while making full use of the
characteristics of the step-down converter by adjusting the number
of the plurality of first capacitors in accordance with the input
voltage of the step-down converter.
[0076] In the voltage converting circuit, the power source may
include a vibration electric power generation device that converts
external vibration energy into electric power or may be a power
source device that is able to supply different electric power.
[0077] The present invention may also be defined from an aspect of
an electronic device including the foregoing voltage converting
circuit. That is, the present invention provides an electronic
device including the voltage converting circuit and the load
circuit. Herein, the voltage converting circuit causes an output
voltage of the power source to step down to a voltage that is
supplied to the load circuit.
DESCRIPTION OF SYMBOLS
[0078] 1 . . . Voltage converting circuit
[0079] 2 . . . First capacitor group
[0080] 5 . . . Switchover control circuit
[0081] 6 . . . Second capacitor
[0082] 8 . . . Step-down converter
[0083] 10 . . . Power source circuit
[0084] 11 . . . Vibration electric power generation device
[0085] 12 . . . Rectification circuit
[0086] 15 . . . Load circuit
[0087] 21 to 23 . . . First capacitor
[0088] 31 to 33 . . . Voltage monitoring circuit
[0089] 41 to 43 . . . Switching adjustment circuit
[0090] 71a, 71b . . . Switching circuit
[0091] 72a, 72b . . . Switching circuit
[0092] 73a, 73b . . . Switching circuit
* * * * *